aio: use new API in example
diff --git a/serial/aio.py b/serial/aio.py
index 7e16545..257c47c 100644
--- a/serial/aio.py
+++ b/serial/aio.py
@@ -97,7 +97,7 @@
         def connection_made(self, transport):
             self.transport = transport
             print('port opened', transport)
-            transport.serial.setRTS(0)
+            transport.serial.rts = False
             transport.write(b'hello world\n')
 
         def data_received(self, data):